The most important thing you need in order to transform a beaded necklace into purse handles is what is called a large eye beading needle. You can find these in the beading isle of most craft stores.
The needle on the left is the large eye beading needle and the needle to the right is a regular sewing needle.
As you can see the needle on the left is basically one large opening with needle like points on each end. This will enable you to thread on the sturdy string (size 10 crochet thread) you need and still be able to thread the needle through the opening in your beads